Mass and heat transport characteristics of full-scale open-cathode air-cooled PEMFC stacks: Comprehensive morphology analysis of flow field aspect ratio and channel configurations

In open-cathode air-cooled proton exchange membrane fuel cell stacks, the flow field are key factors governing oxygen transport, heat transfer, and inter-cell performance uniformity. This study developed a full-scale fuel cell stack model and systematically revealed the effects of the flow field on heat and mass transfer behavior as well as performance distribution within the open-cathode air-cooled stack, and clarified the intrinsic mechanism for the attenuation of optimization effects achieved at the single-cell at the stack. The results show that increasing the flow field aspect ratio at the stack improves oxygen supply and reaction uniformity, mitigates temperature hot spots, and enhances cell voltage uniformity, leading to a peak output voltage increase of 10.5%. Diverging channels enhance downstream and under-rib mass transfer, leading to a performance improvement of 7.6%, whereas converging channels weaken downstream oxygen supply and cause a voltage reduction of 9.34%. When the optimal flow field aspect ratio and channel configuration are both applied at the stack level, more uniform electrochemical reactions exacerbate heat accumulation in the central cells, leading to increased voltage loss. This partially offsets the performance improvement brought by enhanced mass transfer, resulting in an overall performance increase of only 4.3% for the stack. Therefore, for open-cathode air-cooled stack, optimizing heat dissipation is key to unlocking its performance limitations.